Technology for liquid toning of an electrographic latent image on an image bearing surface of a recording medium is well known. Typically, an application roll with auxiliary members is taught for applying a liquid toner or developer as a thin film to the surface of the recording medium. The roll can be submerged partially in a liquid toner (developer) bath and can be rotated at a rate sufficient to cause the developer to produce a thin film on circumferential surfaces of the roll by viscous friction. The recording medium is moved in spaced adjacent relationship to the roll. A layer of liquid toner is maintained across the gap between adjacent surfaces aided by the relative velocities involved, an electric field across the gap, and/or a suitable electrical bias between the members. Examples of such technology are shown in U.S. Pat. Nos. 3,203,395; 3,256,855; 3,367,791; 3,560,204; and 4,141,317; Jap. Utility Model Laid Open Publication 56-35634; and German Offenlegungsschrift 2,238,404.
U.S. Pat. No. 3,798,049, for example, teaches a method for developing a latent electrostatic image by roller application to such image of a viscous liquid thixotropic dispersion of polarizable toner particles in a non-polar vehicle. A thin layer of the dispersion that has a dielectric constant between 100 and 10,000 is spread over the roller's outer surface. Charged toner particles on the roller surface are thus selectively transferred to the surface of the electrostatic image.
To remove excess liquid toner from the surface of a developed image, various techniques have been taught. For example, the aforereferenced Ger. Offen. 2,238,404 describes a drying roll that is rotated in the same direction as the direction of medium movement. U.S. Pat. No. 4,454,833 teaches the use of a drying roll that rotates in a direction opposite to the direction of movement of the recording medium to remove excess toning liquid from the medium surface. U.S. Pat. No. 4,733,273 teaches a roll wiping arrangement that separates excess liquid developer from the recording medium surface. U.S. Pat. No. 4,754,302 teaches a combination of a squeezing roller unit, a recovery blade, and an air knife device.
In general, such prior art methods and apparatus suffer from such disadvantages as low operating speeds, and difficulties in removing and disposing of the relatively large quantities of residual dispersion liquids clinging to the face of the developed image. Production of high resolution toned images is difficult to achieve at high operating speeds.